Stationary or wheeled inclinable seat arrangement, in particular for the sick or handicapped

ABSTRACT

An inclinable seat arrangement, in particular for a sick or handicapped occupant, is described. It comprises a framework ( 2 ) and an inclinable seat ( 3 ) connected to the framework by an articulation ( 4 ) and by a positioning mechanism arranged so as to facilitate the manipulations for inclining the seat by the occupant or by another person. The axis of the articulation ( 4 ) is preferably located proximate a vertical line passing through the center of gravity (G 1 ) of the occupant when in a position corresponding to the equilibrium position of the empty seat. An elastic mechanism, exerting a progressive return couple toward the equilibrium position, comprises elastic bearings ( 24 ) within the articulation. The elastic mechanism also preferably comprises a constant force gas thrustor ( 6 ) which includes a controlled blocking arrangement. In place of the gas thrustor there may be provided a motorized jack ( 51 ) controlled by the occupant ( 48 ). The seat arrangement may be employed in stationary or wheeled chairs for the sick or handicapped.

FIELD OF THE INVENTION

The present invention concerns an inclinable seat arrangement, inparticular for a sick or handicapped occupant, comprising a frameworkarranged to rest on the ground, a seat mounted on the framework by meansof at least one articulation with a horizontal transversal axis, so asto be inclinable within a range of inclined positions, and positioningmeans arranged so as to stabilize the seat in at least one of saidpositions whenever the seat supports the weight of the occupant, inwhich the positioning means include blocking means adapted to block theinclination of the seat in every position within said range and to bemanually controlled, and elastic means coupling the seat to theframework and defining a no-load equilibrium position whenever the seatis not occupied, the elastic means being arranged to exert a returncouple on the seat toward the no-load equilibrium position whenever theseat is in a position different therefrom, the return couple increasingas the seat moves away from said equilibrium position, and in which atleast certain of said elastic means are associated with saidarticulation.

DESCRIPTION OF RELATED ART

Inclinable seat arrangements are known in which the inclination of theseat can be manually modified and blocked by means of an indexing notchmechanism. U.S. Pat. No. 2,986,200 shows for example an invalid'swheelchair in which the tilting articulation of the seat is associatedwith a blocking mechanism and with return springs which oppose thetilt-over couple produced by the weight of the occupant, in order tostabilize the seat and enable manoeuvring thereof with little effort.Nevertheless, such arrangements have not been of commercial importancesince the springs must be relatively strong and do not permit theobtaining of a good concordance between the variation of the returncouple and the variation of the couple due to the weight of theoccupant. It is thus necessary to exert substantial force in order toplace the seat in a position distant from the equilibrium position, orto return it thereto.

Patent application FR 2/693,889 describes a tilting armchair arrangementalso having elastic means associated with the articulation in the formof a torsion spring and blocking means arranged at a distance from thearticulation in the form of a fluid-containing cylinder the piston ofwhich brakes the tilting and includes a blocking valve controlled by theoccupant. When unblocked, the piston cannot contribute to the tilting ofthe seat, but simply opposes any rapid movement thereof. It resultstherefrom that the spring must be relatively strong, as in thepreviously mentioned prior art.

In general, in order to reduce the risk of an undesired tipping over ofa seat of this nature, it is provided that the axis of articulation beplaced in the neighbourhood of a vertical line passing through thecentre of gravity of the occupant. The occupant may then control themovements of inclination by movements of his body, for example of thechest, in order to change the position of his center of gravity and thusproduce tilting of the seat following unblocking. However, it isnecessary that such movements of the body have a certain amplitude whenthe center of gravity is to pass from one side to the other of thesupport articulation. In such case, if they are easy enough for a personin sound health, they may be arduous, indeed impossible, for a sick orhandicapped person. Additionally, premature unblocking or tardyunblocking of the blocking element may lead to brusque manoeuvres andincidents.

Swiss patent 681 772 shows an office chair with an inclinable seatmounted on an elastic articulation provided with rubber elements as wellas an abutment in front and an abutment behind which limit the possiblerange of inclination. There is no means of blocking in intermediatepositions. Such an arrangement is not applicable to a seat for the sickor handicapped. If it were to be adapted to such an application, itwould require particularly strong and heavy elastic elements. Noweconomy in weight is an important criterion in the conception of awheelchair, in particular one for manual propulsion.

For the rest, there is known through patent application GB 2,029,334 atype of inclinable seat arrangement in which the positioning means areformed by a manual or motorized actuator, for example a linearhydraulic, pneumatic or electric jack which controls the spread betweentwo respective points of the framework and of the seat at a certaindistance from the articulation axis. In order that a sick or handicappedoccupant may himself modify the inclination of the seat, the actuatormust be capable of functioning when the seat is occupied, thus bedimensioned in a manner to produce sufficient force in order to overcomethe maximum couple resulting from the weight of the occupant in anyposition whatsoever of the seat. This influences the weight, the volumeand the cost of the positioning means in a negative manner, as well astheir energy consumption. If the actuator is manual, manoeuvres by asick or handicapped occupant may prove quite difficult and taxing.

SUMMARY OF THE INVENTION

The present invention seeks to perfect an inclinable seat arrangement ofthe type indicated in the preamble in a manner to avoid theabove-mentioned drawbacks of the prior art arrangements by facilitatingthe tilting manoeuvres of the seat with a simple construction as lightas possible and inexpensive. According to a particular purpose of theinvention, all the manoeuvres ought to be capable of being effected withrelatively feeble efforts, whether the latter be exerted by the occupanthimself, by another person or by motorized means.

To this end, a first aspect of the invention concerns an inclinable seatarrangement such as defined in the preamble, characterized in that theelastic means further comprise a gas thrustor arranged so as to exert aforce between the framework and the seat at a distance from thearticulation axis, said force being substantially constant, at leastwhen the blocking means are unblocked.

Thus, it is possible to obtain through the combined action of theelastic means associated with the articulation and the force of the gasthrustor a return coupled which varies non-linearly with the inclinationof the seat from the no-load or loaded equilibrium position.Effectively, the moment of the force from the gas thrustor can vary inthe course of the tilting movements of the seat, because the distancebetween the articulation and the axis of the thrustor also varies. Therespective anchor points of the gas thrustor on the framework and on theseat can be chosen in a manner to obtain the appropriate variationminimizing the effort necessary for the manoeuvre throughout the entirerange of inclination. In general, the no-load equilibrium position willbe located rather towards the front and preferably the gas thrustor willbe arranged in a manner such that its force opposes tilting towards therear where the couple due to the weight of the occupant is relativelygreat. Thus, the elastic means incorporated in the articulation may beless strong, less heavy and less expensive.

It must be noted that in the prior art illustrated by the documents U.S.Pat. No. 2,986,200 and FR 2 693 889 cited hereinabove the elastic meansassociated with the articulation exert a return couple which increaseslinearly with the inclination of the seat from the equilibrium position.To the contrary, the couple due to the weight of the occupant does notvary linearly, but according to a sine law relative to the inclination.This is why good correspondence between these two couples within therange of useful inclinations is not obtained with the arrangements ofthe prior art. The invention defined hereinabove enables overcoming thisdrawback by an appropriate choice of the anchor points of the gasthrustor.

Preferably, the blocking means are associated with the gas thrustor andarranged so as to block or unblock the latter on command, the gasthrustor being of a type of substantially constant force when unblocked.Since the gas thrustor serves at the same time as elastic means andblocking means, this represents an economy of material and weight. Whenit is blocked, the thrustor exerts the force of reaction necessary inorder to maintain the seat in the chosen position.

The second aspect of the invention concerns an inclinable seatarrangement such as defined in the preamble, characterized in that thepositioning means include a jack with a motorized drive arranged at adistance from the articulation axis, said jack coupling the framework tothe seat in order to control the inclination of the seat and formingpart of the blocking means.

In such an arrangement thus disposed, the combination of the elasticmeans associated with the articulation and of the motorized jackassuring at the same time the positioning and the blocking of the seatin any position whatsoever within the range of inclination, offersseveral advantages. Thanks to the elastic return couple, there can beemployed a jack the force and the energy consumption of which aregreatly reduced. This, thus, permits the fitting out of a stationaryseat or a wheelchair with manual propulsion, the jack being for examplean electric jack energized by a battery or a small accumulatorincorporated in the arrangement according to the invention. On the otherhand, the arrangement includes few components since the jack fulfils thetwo functions of positioning and blocking. These components can besimple, small, light and relatively inexpensive.

Preferably, the axis of articulation is located proximate a verticalline passing through the center of gravity of the occupant when the seatis in said no-load equilibrium position. The seat is preferablyinclinable towards the front and towards the rear relative to theno-load equilibrium position.

In a preferred embodiment of the arrangement, the elastic means compriseat least one elastic bearing forming said articulation and includingrubber elements arranged so as to produce at least a portion of thereturn couple.

Furthermore, it may be provided that the seat includes a baseplatemounted on the framework and a back support mounted in an inclinablemanner on the baseplate by means of another articulation associated withelastic return means loading the back support.

In a particularly advantageous application of the invention, thearrangement is provided in the form of a wheelchair or of a push chairfor the sick or handicapped. Preferably the framework includes twoprincipal wheels arranged along a common central axis located proximatea vertical line passing through the common center of gravity of thearrangement and occupant, at least one directable front wheel located infront of the central axis and at least one rear safety roller arrangedso as to bear on the ground, at least in case of tilting over of thearrangement towards the rear around the central axis. Said rear rollercan advantageously be adjustable in height on the framework to which itis coupled by elastic return means adapted to press it onto the ground,at least when the arrangement tends to tilt over towards the rear aroundthe central axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willappear from the following description of a preferred embodiment thereofpresented by way of example having reference to the attached drawings:

FIG. 1 is a lateral schematic view of an arrangement according to theinvention, the seat of which is found in a loaded equilibrium position;

FIG. 2 is a schematic view from the rear of the arrangement;

FIG. 3 shows in perspective an element forming an elastic bearing in thearrangement of FIGS. 1 and 2, and

FIG. 4 is a schematic diagram showing a typical example of thecharacteristic curve of the pivoting couple-angle of an elastic bearingaccording to FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT

The inclinable seat arrangement according to the invention such as it isshown on FIGS. 1 and 2 is embodied in the form of a push chair for thesick or handicapped. However, the same principle of construction couldbe applied to a stationary seat or to a wheelchair, whether the latterbe propelled by the occupant himself or by a motorized driveincorporated in the chair.

The push chair 1 as shown includes a lower framework 2 and an inclinableseat 3 which are coupled by an articulation 4 with horizontal axis 5 andby a retaining element which, in the present case, is a gas thrustor 6provided with an incorporated blocking arrangement.

The framework 2 principally includes a rigid chassis made up oflongitudinal metallic tubes 10, 11, transversal tubes 12 and verticaltubes 13, 14, two principal side wheels 15 centered on a commontransversal axis 16 and two front wheels 17 freely directable around avertical axis, wheels 15 and 17 resting on the ground 18 in order tosupport the push chair assembly under normal conditions. The twoprincipal wheels 15 are mounted on an axle 19 which is secured to thechassis, preferably in a longitudinally adjustable position. At theback, the framework 2 further includes two elbowed props 20, eachbearing a rear security roller 21 which normally is found slightly abovethe ground 18, but which can bear thereon to prevent a possible tippingover of the chair towards the rear around axis 16 if front wheels 17 arelifted up for any reason whatsoever. In this example, the props 20 arefitted into the horizontal tubes 10 of the chassis where they aresecured in a longitudinally adjustable position. It will be noted thatframework 2, according to a variant, could include a single front wheel17 and/or a single rear roller 21. It will also be noted that such aframework could be fitted out with a motorized driving system actuatingthe principal wheels 15 in the case of a motorized wheelchair. Thisframework could also be that of a manually driven wheelchair if theprincipal wheels 15 were arranged in view thereof, in particular with anannular hand grip within reach of the occupant's hand.

The chassis of framework 2 further includes two supports 22 on which aresecured by means of metallic clamps 23, two pivoting elastic bearings24, to be described hereinafter, and which are aligned on axis 5 inorder to form together the articulation 4.

Seat 3 includes a rigid metallic chassis 26 supporting an upholsteredchair 27 on which the occupant 28 may take his place. In front, chassis26 bears an adjustable foot rest 29. At the back, it bears two inclinedarms 30 provided with handles 31 in order to permit an auxiliary personto displace and direct the push chair 1. One of the handles 31 isprovided with a hand grip 32 which controls, for example, the unblockingof the gas thrustor 6 thanks to a cable transmission 33. Preferably, thearms 30 are fixed to the back rest 34 of the chair 27 and are mounted onthe chassis 26 by means of a pair of articulations 35 enablingadjustment of the inclination of the back rest relative to the baseplate36 of the chair. Such articulations can also include elastic returnmeans, for example elastic elements analogous to those of the bearings24. In order to permit readjustment of the position of the center ofgravity of the seat and of the occupant as a function of the position ofthe back rest, there may be provided a longitudinal translationarrangement of the chassis 26 relative to the articulation 4, forexample by means of a crank actuating a screw and nut mechanism.

FIG. 3 shows the structure of one of the elastic bearings 24 forming thearticulation 4. In this example, it concerns a ROSTA (registeredtrademark) elastic element of the type DR-S, manufactured by the companyROSTA-WERK AG in Hunzenschwil (Switzerland). This element includes asquare outer tube 40 of steel, a square interior tube 41 likewise ofsteel arranged within the outer tube without touching it, and fourprismatically formed blocks 42 of rubber having an approximatelytriangular cross-section. The blocks 42 are arranged in the corners ofthe outer tube 40 and each bears on a face of the interior tube 41 whichin its rest position is rotated 45° relative to the outer tube 40, theblocks 42 being lightly compressed between the two tubes. When tube 40is fixed, this assembly elastically supports the interior tube 41 in alldirections and permits it to pivot from the rest position through anangle ±α around an axis 5, such angle a being capable of reaching atleast 30°. In the present case, one end of tube 41 of each elasticbearing 24 is secured to the chassis 26 of the seat by means of ametallic clamp 44. The rubber blocks 42 exert a return couple M on tube41 which increases progressively with the angle α. As shown on FIG. 4,this progression is not linear, the variation of the couple M beingrelatively small for the smaller values of the angle α and considerablyhigher when the angle becomes greater. Furthermore, the stress-straindiagram of the rubber blocks exhibits a hysteresis which is translatedby a spread between the loading curve 61 and the unloading curve 62 inFIG. 4. Thus, the elastic bearing 24 also constitutes a shock absorberfor all the vibrations of one tube 40, 41 relative to the other, intranslation as well as in rotation.

In the embodiment described here, the thrustor 6 is a gas spring ofconstant force and automatic blocking of the type BLOC-O-LIFT(trademark) manufactured by the company STABILUS in Koblenz (Germany).When it is unblocked, it exerts a constant thrusting force F of 500 N.Its lower end is hinged on a support 45 fixed to a transverse beam 46secured to the tubes 10 of the chassis in an adjustable position. Itsupper end is hinged at 47 to a rear end of the chassis 6 of the seat.

Since the thrustor 6 is always found at a certain distance from thearticulation axis 5, its force produces a permanent couple which tendsto return the seat to an upright position. When the latter is notoccupied, such couple causes the seat to swing towards the front and theelastic bearings produce an increasing resistance couple until the twocouples are balanced, thus defining a no-load equilibrium position ofthe seat. This position is adjustable, in particular by displacing thetransverse beam 46 which also permits modifying the couple produced bythe force F relative to the axis 5 of articulation 4.

It will be noted nevertheless that the gas thrustor 6 need notnecessarily be provided with a blocking arrangement. The latter could bean element separate from the thrustor, for example in the form describedin patent application FR 2,693,889. However, the combination describedhere has the advantage of uniting the two functions of return and ofblocking in a single element which represents an improvement in weightand of space taken up.

Preferably, the position of the articulation 4 relative to seat 3 issuch that when occupant 28 normally rests on the seat, a vertical lineg1 passing through the center of gravity G1 of the occupant passesproximate the axis 5 of the articulation, at least when the seat isfound in the position referred to as the no-load equilibrium position.In this position, the seat is preferably rather upright in order thatthe footrest 29 not be too high and that the occupant can easily sitdown. It is then preferable that the vertical line g1 be found slightlybehind the axis of articulation 5 so that it is sufficient to unblockthe thrustor 6 in order that the seat be automatically inclined towardsthe rear under the effect of the couple produced by the weight of theoccupant. If the thrustor 6 is maintained unblocked by means of the handgrip 32, the seat 3 is stabilized in a loaded equilibrium position inwhich the couple due to the weight of the occupant is counterbalanced bythe couple resulting from the elastic elements 6 and 24. There resultstherefrom a loaded equilibrium position specific to each position of theoccupant. In order to define another inclination position, it issufficient to raise or lower the handles 31 and to release the lever 32in order to block the thrustor 6 when the desired position is attained.

In a variant shown in dashed outline on FIG. 2, the unblocking controlof thrustor 6 can also include a control handle 48 arranged on the seat3 in a manner to be accessible to the occupant in order that the lattercan himself manoeuvre the seat. This control replaces that of the handgrip 32 in the case of a wheelchair. When the occupant himself wishes tomodify the inclination of seat 3, he modifies, if necessary, theposition of his center of gravity G1 by displacing a portion of hisbody, for example in slightly advancing his head, his chest or an arm,if he wishes to tilt forwardly, and he unblocks the thrustor 6. Thechange in the couple due to his weight which results therefrom thenproduces the desired movement until the return couple of the elasticelements has changed sufficiently to maintain the seat in the new loadedequilibrium position, even if the vertical line g1 has not changed sidesrelative to the articulation axis 5. Consequently, even a weak orhandicapped sick person can modify without effort the inclination of hisseat.

In FIG. 1, it will be noted that the central axis 16 of the principalwheels 15 is located proximate a vertical line g2 passing through thecommon center of gravity G2 of the arrangement 1 and of the occupant 28,such vertical line being slightly in front of the axis 16 for everyposition of seat 3 in order that the front wheel 17 bear on the ground.Thus, it is easy to cause tilting of the assembly of arrangement 1towards the rear, including its framework 2, around axis 16 in order tolift the front wheels when they must cross over an obstacle such as athreshold or the edge of a sidewalk. Tilting is then stopped by the rearrollers 21. The arms 20 can also be mounted on framework 2 in an elasticmanner, for example by means of ROSTA elastic elements analogous tothose of the bearings 24 and forming an articulation 50 (FIG. 1) with ahorizontal axis in a manner such that each roller 21 is movable inheight on the framework according to a principle described in the patentapplication WO 96/15752 from the same applicant. In this case, rollers21 can bear lightly on the ground, even in the normal position of theframework in conformity with FIG. 1 in which the front wheels 17 alsotouch the ground and their bearing force will increase if the assemblyof the arrangement has a tendency to tilt over backwards. In combinationwith such a progressive elastic support of the rear roller or rollers21, an inclinable seat according to the present invention permits usinga change of inclination of the seat in order to displace easily thecenter of gravity of the occupant so as to produce a transfer of theload on the front wheels to the rear rollers or vice versa, inparticular in order to benefit from the elasticity of the support on therear rollers. For example, when the occupant of such a wheelchair,motorized or not, must go down a path with a steep slope, he can inclinehis seat towards the rear, on the one hand in order to compensate forthe inclination of the framework towards the front by reason of theslope of the ground, and, on the other hand, in order to unload thefront wheels and place a greater load on the principal wheels which arethose on which he has the actuating means for the propulsion, thebraking and the direction of his wheelchair. By further accentuating theinclination, he can even cause tilting over of the framework towards therear in order to lift the front wheels, for example in order to causethem to pass over an obstacle. The potential energy thus accumulated inthe return springs of the rear rollers 21 is reusable when thewheelchair is once again set upright, in particular in order tofacilitate the climbing of the main wheels onto the obstacle. Thisphenomenon and its advantageous application are described in detail inthe previously cited patent application.

The person skilled in the art will understand that if the gas thrustor 6described hereinabove were replaced by a simple blocking element, thatis to say if the constant thrust exerted by such thrustor were omitted,the return couple would then be produced solely by the elastic bearings24. However, the thrustor 6 has the advantage of exerting a pre-stresson the elastic bearings from whence there results a stronger returncouple as soon as the seat departs from its equilibrium position.Additionally, it will be recalled that the choice of the position of thethrustor 6 enables adjusting its distance from the articulation axis andthus modulating the couple produced by its force F.

Another variant consists in forming the articulation 4 by means ofordinary bearings, the return couple then being assured by one orseveral spring elements coupling the seat 3 to the framework 2, forexample with a torsion spring associated with the articulation 4.

In the application to a motorized wheelchair, it is possible to replacethe thrustor 6 described hereinabove by a linear or rotating motorizedactuator, for example an electric jack 51 controlled by the occupant inorder to modify and block any position of inclination whatsoever of seat3. Such jack 51 also serves as blocking element which maintains theposition of seat 3. In FIG. 1, there has been shown by way of indicationa control housing 52 for jack 51 mounted on the seat 3 within reach ofthe hand of the occupant 28 and an electric battery 53 mounted on theframework 2 in order to energize jack 51. The housing 52 includespush-pieces or a hand lever in order to control the jack 51. Thanks tothe elastic return means, such an actuator can have a reduced nominalforce relative to known arrangements, which permits an improvement inweight, volume and the cost of manufacture as well as economies ofenergy of operation.

In another variant, not shown, the arrangement can be stationary and notprovided with wheels. In this case, the framework 2 can be a simplebaseplate resting on the ground, or generally any structure whatsoeverapt to support seat 3 and articulation 4, for example in a medical ordental practice or in a vehicle.

What is claimed is:
 1. An inclinable seat arrangement comprising aframework arranged to rest on the ground, a seat mounted on theframework by at least one articulation with a horizontal transverse axisso as to be inclinable in a range of inclined positions, and positioningmeans for stabilizing arranged so as to stabilize the seat in at leastone of said positions when the seat supports the weight of the occupant,wherein said positioning means include manually controlled blockingmeans for blocking the inclination of the seat in every position withinsaid range and elastic means for coupling the seat to the framework anddefining a no-load equilibrium position when the seat is not occupied,the elastic means being arranged to exert a return couple on the seattoward the no-load equilibrium position whenever the seat occupies aposition different from the equilibrium position, the return coupleincreasing as the seat is moved away from said equilibrium position, andwherein said elastic means comprise at least one elastic bearing formingsaid articulation and including rubber elements arranged to produce atleast a part of said return couple, and wherein said elastic meansfurther comprise a gas thrustor arranged to exert a force between theframework and the seat at a distance from the articulation axis, saidforce being substantially constant at least when the blocking means areunblocked.
 2. The inclinable seat arrangement of claim 1, wherein theseat includes a sole plate mounted on the framework and a back supportinclinably mounted on the sole plate by means for acting on the backsupport.
 3. The inclinable seat arrangement of claim 1, wherein theblocking means are associated with the gas thrustor and arranged so asto block or unblock the gas thrustor upon command, and the gas thrustorexerts a substantially constant force when it is unblocked.
 4. Theinclinable seat arrangement of claim 3, wherein the seat includes a soleplate mounted on the framework and a back support inclinably mounted onthe sole plate by another articulation associated with elastic returnmeans for acting on the back support.
 5. An inclinable seat arrangementin the form of a wheelchair for the sick or handicapped comprising; aframework arranged to rest on the ground, a seat mounted on theframework by at least one articulation with a horizontal transverse axisso as to be inclinable in a range of inclined positions, and positioningmeans for stabilizing the seat in at least one of said positions whenthe seat supports the weight of the occupant, wherein said positioningmeans include manually controlled blocking means for blocking theinclination of the seat in every position within said range, and elasticmeans for coupling the seat to the framework and defining a no-loadequilibrium position when the seat is not occupied, the elastic meansbeing arranged to exert a return couple on the seat toward the no-loadequilibrium position whenever the seat occupies a position differentfrom the equilibrium position, the return couple increasing as the seatis moved away from said equilibrium position, said elastic meanscomprise at least one elastic bearing forming said articulation andincluding rubber elements arranged to produce at least a part of saidreturn couple, the positioning means comprise a jack with a motorizeddrive arranged at a distance from the axis of the articulation, saidjack coupling the framework to the seat in order to control theinclination of the seat and forming part of the blocking means, theframework includes two principal wheels arranged along a common centralaxis located proximate a vertical line passing through the common centerof gravity of the arrangement and of the occupant, at least onedirectable front wheel located ahead of the central axis, and at leastone rear safety roller arranged so as to bear on the ground at least inthe event of tipping over of the arrangement toward the rear about thecentral axis, and said rear roller is movable upwardly on the frameworkto which it is connected by elastic return means for pressing it ontothe ground at least when the arrangement tends to tip over toward therear about the central axis.
 6. The inclinable seat arrangement of claim5, wherein the seat is inclinable toward the front and toward the rearrelative to the no-load equilibrium position.
 7. The inclinable seatarrangement of claim 5, wherein the seat includes a sole plate mountedon the framework and a back support inclinably mounted on the sole plateby another articulation associated with elastic return means for actingon the back support.
 8. The inclinable seat arrangement of claim 1,wherein the seat is inclinable toward the front and toward the rearrelative to the no-load equilibrium position.
 9. The inclinable seatarrangement of claim 1, wherein the seat includes a sole plate mountedon the framework and a back support inclinable mounted on the sole plateby another articulation associated with elastic return means for actingon the back support.
 10. The inclinable seat arrangement of claim 1, inthe form of a wheelchair for the sick or handicapped.
 11. The inclinableseat arrangement of claim 8, wherein the framework includes twoprincipal wheels arranged along a common central axis located proximatea vertical line passing through a common center of gravity of thearrangement and of the occupant, at least one directable front wheellocated ahead of the central axis, and at least one rear safety rollerarranged so as to bear on the ground at least in the event of tippingover of the arrangement toward the rear about the central axis.
 12. Theinclinable seat arrangement of claim 11, wherein said rear roller ismovable upwardly on the framework to which it is connected by elasticreturn means adapted to press it onto the ground at least when thearrangement tends to tip over toward the rear about the central axis.13. An inclinable seat arrangement comprising a framework arranged torest on the ground, a seat mounted on the framework by at least onearticulation with a horizontal transverse axis so as to be inclinable ina range of inclined positions, and positioning means arranged forstabilizing the seat in at least one of said positions when the seatsupports the weight of an occupant, wherein said positioning meansinclude manually controlled blocking means for blocking the inclinationof the seat in every/position within said range, and elastic means forcoupling the seat to the framework and arranged to exert a return coupleon the seat, wherein said elastic means comprise at least one elasticbearing forming said articulation and arranged to produce at least apart of said return couple, and wherein said elastic means furthercomprise a gas thrustor arranged to exert a force between the frameworkand the seat at a distance from the articulation axis, said force beingsubstantially constant at least when the blocking means are unblocked,and wherein said blocking means are associated with said gas thrustorand arranged so as to block or unblock the gas thrustor upon command.14. The inclinable seat arrangement of claim 13, wherein the seat isinclinable toward the front and toward the rear relative to a no-loadequilibrium position.
 15. The inclinable seat arrangement of claim 13,wherein the seat includes a sole plate mounted on the framework and aback support inclinably mounted on the sole plate by anotherarticulation associated with elastic return means for acting on the backsupport.
 16. The inclinable seat arrangement of claim 13, in the form ofa wheelchair for the sick or handicapped, wherein the framework includestwo principal wheels arranged along a common central axis locatedproximate a vertical line passing through the common center of gravityof the arrangement and of the occupant, at least one directable frontwheel located ahead of the central axis, and at least one rear safetyroller arranged so as to bear on the ground at least in the event oftipping over of the arrangement toward the rear about the central axis;said rear roller being movable in height on the framework to which it isconnected by an elastic return means adapted to press it onto the groundat least when the arrangement tends to tip over toward the rear aboutthe central axis.